linux-kernel - [PATCH 01/23] dma-mapping: provide a generic DMA_MAPPING

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Date:   Fri, 30 Nov 2018 14:22:09 +0100
From:   Christoph Hellwig <hch@....de>
To:     iommu@...ts.linux-foundation.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Jon Mason <jdmason@...zu.us>, Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>, x86@...nel.org,
        linux-alpha@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-ia64@...r.kernel.org, linux-parisc@...r.kernel.org,
        xen-devel@...ts.xenproject.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 01/23] dma-mapping: provide a generic DMA_MAPPING_ERROR

Error handling of the dma_map_single and dma_map_page APIs is a little
problematic at the moment, in that we use different encodings in the
returned dma_addr_t to indicate an error.  That means we require an
additional indirect call to figure out if a dma mapping call returned
an error, and a lot of boilerplate code to implement these semantics.

Instead return the maximum addressable value as the error.  As long
as we don't allow mapping single-byte ranges with single-byte alignment
this value can never be a valid return.  Additionaly if drivers do
not check the return value from the dma_map* routines this values means
they will generally not be pointed to actual memory.

Once the default value is added here we can start removing the
various mapping_error methods and just rely on this generic check.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 include/linux/dma-mapping.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 0f81c713f6e9..46bd612d929e 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -133,6 +133,8 @@ struct dma_map_ops {
 	u64 (*get_required_mask)(struct device *dev);
 };

+#define DMA_MAPPING_ERROR		(~(dma_addr_t)0)
+
 extern const struct dma_map_ops dma_direct_ops;
 extern const struct dma_map_ops dma_virt_ops;

@@ -576,6 +578,10 @@ static inline int dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
 	const struct dma_map_ops *ops = get_dma_ops(dev);

 	debug_dma_mapping_error(dev, dma_addr);
+
+	if (dma_addr == DMA_MAPPING_ERROR)
+		return 1;
+
 	if (ops->mapping_error)
 		return ops->mapping_error(dev, dma_addr);
 	return 0;
-- 
2.19.1